Production tubing within a well bore requires periodic maintenance to remove paraffin deposits that could restrict production. These deposits are generally the result of changing pressures and temperatures within a production system and the removal of these deposits is accomplished through a technique known as hot oiling in which heated fluids, typically oil, are circulated through the production system. As will be appreciated by those skilled in the art, hot oiling has other applications and the use of the system described and claimed below is not limited to any particular application. Moreover, the term “hot oiler” is itself merely generic, and the below described system can be used to heat different fluids for different applications including, but not limited to water, treatment fluids used for well stimulations and chemicals or virtually any other fluids requiring heating.
Standard hot oilers are diesel fired units that use an open flame to create the heat needed to heat the batch oil. This flame heats pipes that are in direct contact with it as the batch fluid to be heated flows through the pipes for thermodynamic heat exchange. Heating is performed at or close to atmospheric pressure.
Several problems exist, however, with open combustion burners. The use of open flame is less controlled compared to the use of flameless systems. Exhaust gasses are often hotter in an open combustion system and if they are not monitored these systems can flood and expel flame. The temperatures can reach instantaneous temperatures greater than that of the kindling temperatures of natural gas. This means that if there was a natural gas leak, an ignition point is present. A diesel or propane leak in the vicinity of the burner can also be ignited.
Further, the combustion process in open flame systems is not as complete as in closed systems, and free radicals thereby escape into the atmosphere. Closed combustion engines have compression ratios commonly 14 times greater than open combustion burners. This lack of compression negatively affects the reactiveness of oxygen. Hydrocarbon/oxygen reactions are exothermic which provides the heat energy used by the hot oiler. Provided that the combustion is given enough oxygen, heat and time to complete the process, carbon dioxide and water are produced, which are more benign byproducts. However, nitrogen gas is also present during combustion and if the reaction is not ideal, some molecules of nitrogen attach themselves to oxygen to produce the poisonous gas NO. This gas is referred to as a free radical. Incomplete combustion also produces carbon monoxide which also is a pollutant. NO and carbon monoxide are well recognized as being harmful to the environment.
Open flame systems also require more fuel than flameless systems. Fuel is burned less efficiently in these systems, requiring a greater amount of fuel to produce an equivalent amount of heat in a flameless system.
Open flame units moreover are mandated by regulation to be kept at a predetermined safe distance from the wellhead. This presents the disadvantage that more tubing is required to bring the heated fluid to the well bore.